The present invention relates generally to a method and device for inducing visual sensations within persons suffering from blindness, and, in particular to a method and device for restoring some visual function within the eyes of blind persons by encircling the optic nerve with a self sizing cuff electrode which is electrically stimulated.
Blindness is an affliction which affects more that 42 million persons worldwide. Many causes of blindness, especially those involving occlusions or opacity in the optical pathway through the eye, have yielded to medical treatments and vision can now be restored to a great extent in a large number of cases. Some diseases of the eye, however, cause blindness by attacking the light sensing retina, causing blindness while the remainder of the optical pathway remains functional. A variety of retinal diseases, for example, cause vision loss or blindness by destruction of the choroid, choriocapallaris, and the outer retinal layers. In several retinal degenerative diseases, select populations of photoreceptor cells are lost. Specifically, in macular degeneration and retinitis pigmentosa, the retinal photoreceptors degenerate while other cells in the retina as well as the retina""s central connections are maintained; the complex synaptic interconnections at the outer plexiform layer of the eye that would normally transmit photosignals to the nerve ganglions are intact, as are the ganglion axons or bundles which make up the optic nerve, which normally transmits the visual information to the brain.
Numerous efforts have been made over the years to develop devices which could help to remedy retinal blindness. In the 1930""s, Forester investigated the effect of electrically stimulating the exposed occipital pole of one cerebral hemisphere. He found that when a point at the extreme occipital pole was stimulated, the patient perceived a small spot of light directly in front and motionless, which spots are known as phosphenes. Subsequently, in the 1960""s Brindley and Lewin thoroughly studied electrical stimulation of the human occipital cortex. By varying the stimulation parameters, the investigators described in detail the locations of the phosphenes produced relative to the specific region of the occipital cortex stimulated. These experiments demonstrated: the consistent shape and position of phosphenes; that increased stimulation pulse duration made phosphenes brighter; and that there was no detectable interaction between neighboring electrodes which were as close as 2.4 mm apart.
In recent years, several alternative procedures have been proposed for the restoration of vision. One procedure involves the implantation of a tissue graft or cells into the host retina. One example of this procedure is taught in U.S. Pat. No. 5,817,075.
Another procedure which as been attempted uses electrodes or electrical fields in combination with photosensitive devices to stimulate neurons or ganglion cells. For example, U.S. Pat. No. 4,628,933 is directed to a visual prosthesis having a close packed array of photosensitive devices which are coupled to a plurality of electrodes that stimulate neurons at the surface of the retina in a pattern corresponding to the illumination pattern of the photosensitive array. U.S. Pat. No. 5,109,844 describes a retinal microstimulator for stimulating retinal ganglion cells by the use of a plurality of electrodes for recognition. U.S. Pat. No. 5,147,284 teaches an electromagnetic field radiator and receiver which produce an effect of electrostimulation of the optic nerve and retina by a pulsed magnetic field. Finally, U.S. Pat. No. 5,873,901 uses a thin film optical detector based on a dielectric capacitor that can be implanted onto the retina which can produce a signal at the brain down from the optic nerve that may be perceived as light.
A great variety of electrodes have been developed for application of electrical stimulation. Electrodes intended to stimulate motor nerve fibers include electrodes placed on the surface of the skin, percutaneous intramuscular electrodes, surgically implanted intramuscular electrodes, and epimysial electrodes, while electrodes placed directly on or in peripheral nerve trunks include epineural electrodes, penetrating epineural electrodes, wire and silicon intraneural electrodes.
A different hurdle in the development of a visual prosthesis has been the development of an electrode suitable for chronic implant which can provide stimuli to the optic nerve. The present invention overcomes these and other problems by the use of a self-sizing spiral cuff electrode around the optic nerve.
It is therefore an object of the present invention to provide a method of inducing visual sensation within blind persons by generating electrical stimuli to the optic nerve via a self-sizing spiral cuff electrode.
It is also an object of the present invention to provide a device which can be implanted intracranially within a patient.
It is a further object of the present invention to produce localized visual sensations in blind persons which can be varied by changing the magnitude of the stimulus.
These and other objects of the present invention are accomplished by the use of a signal generating means which transmits a series of pulses to the optic nerve of a blind patient via a self-sizing cuff electrode to activate the nerve, whereby the patient is able to visualize a series of phosphenes with broad distribution within the visual field.